Ok, thanks for those who have replied. Here is the situation as it stands. I have stripped down, cleaned, lubed, re-assembled and performed some limited testing on the head only and so far so good. The inside of the solenoid chamber was visually clean before the process was commenced. There was a fair amount of rust on the metal chamber that houses the solenoid in the head, however this does not come in direct contact with the 02.
So, tomorrow night I will re-assemble the unit and take it for a dunk. If you haven't heard from me by Sunday - then Rick you were right
Cheers,
Ben.